[ath9k-devel] Operation in 1x2 MIMO/antenna configuration

[ath9k-devel] Operation in 1x2 MIMO/antenna configuration

[Philipp Hofmann]

Hi,

I have a question concerning the impact of MIMO/antenna configuration on performance (throughput/range). We have a system with an AR9220 chip running 802.11a in ad-hoc mode. An amplifier with an output power of several watts is connected to one of the two antenna ports.

Hence, effectively we are running the system in a 1x2 MIMO/antenna configuration rather than the specified 2x2 configuration (at least for ranges that can not be reached with standard output power). Obviously, the performance will be decreased compared to a 2x2 configuration with amplifiers connected to each antenna port as, e.g., spatial multiplexing can not be used in a 1x2 configuration.

My question now is whether running a system specified for 2x2 configuration in a 1x2 configuration yields a performance that is lower than the one of a system that was designed for 1x1 configuration only (i.e., no MIMO)? Why this could be the case: the system assumes to be in a 2x2 configuration and sends data on both tx-antenna ports. However, only the data stream of the amplified antenna port reaches the receiver and the data of the un-amplified port gets lost in space.

If this really yields a performance lower than the one of a 1x1 system, it would be necessary to tell the AR9220 chip to use one antenna port only for transmission and hence possibly disable MIMO features that require multiple tx-antennas. Does ath9k have such a possibility/switch?

The reason to use more than one rx-antenna is to make use of maximum ratio combining at the receiver side to increase range.

Cheers,
Philipp
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